1. Field of the Invention
The present invention relates to the production of aluminum nitride via the carbonitriding of alumina, and, more especially, to a continuous such process.
2. Description of the Prior Art
It is known to this art to produce aluminum nitride via the carbonitriding of alumina in a fluidized-bed reactor (see, for example, published European Patent Application 0,266,927, published Japanese Application 63/297,205 and published British Patent Application 87/00,208).
It is also known to this art to carry out the reaction in a rotary kiln (see, for example, published Japanese Patent Applications 62/278,109, 62/20,030 and 61/74,635).
It too is known to produce aluminum nitride in a shafted kiln fitted with a stack of travelling buckets (see, for example, published European Patent Application 0,272,377), or fixed (Japanese Patent No. 1,290,562).
These various prior art processes nonetheless present a certain number of drawbacks. On the one hand, they share the disadvantage of only a single limited production and limited productivity, since the working volume of the reactor is always low.
On the other hand, the resulting final products are generally characterized by their heterogeneity due to a wide distribution in the residence times of the reactants in the kiln. This is particularly the case for the rotary kiln and for the fluidized-bed reactor operating continuously.
It has also been proposed to carry out the reaction in a continuously operating methodical or moving-bed reactor (see published European Patent Application 0,519,806 and WO-92/16,467). These processes permit attaining a production close to one kilogram, or indeed several kilograms of aluminum nitride per hour. However, the productivity of these reactors remains low.
Thus, serious need continues to exist in this art for a high-productivity process for the preparation of AlN, while at the same time maintaining both a high level of production and a great homogeneity of the final product.